The present invention relates to a method and apparatus for measuring moisture, and particularly to an improved method and apparatus which is less sensitive to the positioning of material in which the moisture is to be measured than prior art devices.
Moisture measuring devices of the prior art typically employ some kind of contacting means for making a conductive connection with material in which moisture is to be measured so that the moisture can be determined by electrical conduction. Unfortunately, the contacting means or brushes are subject to breakage and shorting whereby the moisture indications tend to become inaccurate. Further, even if the brushes are in good condition, the degree of electrical contact provided with the material under test is non-uniform.
Moisture detectors have been developed which do not require contact with the material but instead employ capacitive coupling or the like. Many, however, are quite sensitive to the position of the material relative to the sensor conductor, as well as to the thickness of the material, and therefore indications derived on a production line basis can be somewhat undependable. Also, the conveying means upon which the material is transported can short out the measuring system such that a dependable reading is not obtained.
In my prior U.S. Pat. No. 4,377,783, a measuring system is set forth in which transmitting and receiving plates are offset along the path of the measured material, and a conductive path in the veneer and the grounded conveyor is employed as part of the circuit. While very efficacious, there is again some dependency upon accurate contact with the material being measured. It would also be desirable to provide a moisture measuring method and apparatus which is almost entirely independent of positioning of the material so that the measurement is even less subject to such factors as warp, thickness and the like. Almost all prior art devices have some dependence upon these factors, and also to unwanted grounding of the material as mentioned above.